The Green Party could oppose plans for a high speed rail line between London and Birmingham after delegates meeting in Birmingham heard claims it would cause global warming.

High speed rail is often portrayed as an environmentally-friendly policy, and supporters claim it will reduce air travel and car use by encouraging travellers to take the train for long distance journeys.

But some environmentalists argue it will encourage people to make unnecessary journeys, and money could be better spent on improving local services.

High speed rail also uses more energy and creates more carbon emissions, which are believed to cause global warming, than conventional trains.

The Green Party conference, at Birmingham Conservatoire, discussed a motion arguing that “support for high speed rail is not compatible with creating a fair and just society, not compatible with the central tenet of sustainable transport which is to reduce the need to travel, not compatible with the urgent need to reduce greenhouse gas emissions and not compatible with the need to reduce energy and land take for transport purposes.”

Delegates voted to “refer back” the motion, which means it will be discussed again at future gatherings.

It marks a break with the party’s previous policy, which was to support high speed rail lines between London and Birmingham.

The Government wants to build a new 250 mph line between the capital and the West Midlands as the first stage of a new national network, eventually reaching Manchester and Scotland.

But the plans have sparked opposition in some of the towns and villages next to the proposed line, in places such as Warwickshire, Staffordshire and the Chilterns.

All three major parties back high speed rail but the smaller parties are expressing doubts.

West Midlands UKIP MEP Mike Nattrass, a member of the EU transport committee, has also come out against high speed lines. He said: “I just think this is an unnecessary project which destroys the countryside for the sake of saving 30 minutes.”

He added: “Why are we doing this when people need to work where they live, not all be sucked down to London? If this happens we’ll have people commuting even further distances and we just don’t need it.”